The present invention relates to soft-magnetic hexagonal ferrite composite particles, and a green sheet using the same and a soft-magnetic hexagonal ferrite sintered ceramics. More particularly, the present invention relates to soft-magnetic hexagonal ferrite composite particles comprising soft-magnetic hexagonal ferrite particles, and barium carbonate particles and/or strontium carbonate particles; a green sheet using the soft-magnetic hexagonal ferrite composite particles; and a soft-magnetic hexagonal ferrite sintered ceramics using the soft-magnetic hexagonal ferrite composite particles which is produced by forming the soft-magnetic hexagonal ferrite composite particles into a compact and then sintering the compact, and which exhibits a high sintering density and a high volume resistivity as well as such frequency characteristics that an imaginary part of permeability thereof is not more than 1 at 400 MHz and becomes large at a frequency near several GHz, while a real part of permeability is kept substantially constant without lowering the real part in a frequency range of from low frequency to several hundreds MHz.
As well known in the arts, soft-magnetic cubic spinel ferrite sintered ceramics show a high imaginary part of permeability in a frequency range of several hundreds MHz, and, therefore, have been used as impedance elements for attenuating noises over a frequency range of several hundreds MHz due to magnetic loss thereof caused in such a frequency range, or electromagnetic wave absorbers for absorbing electromagnetic waves.
In addition, the soft-magnetic cubic spinel ferrite sintered ceramics show a constant real part of permeability over a frequency range of from low frequency to several tens MHz and, therefore, have also been widely used as inductor elements owing to a high inductance thereof.
With the recent development and progress of mobile communication systems such as portable telephones and PHS as well as high-speed digital devices for indoor use such as wireless LAN, personal computers and game devices, it has been rapidly attempted to apply signals having a frequency range of several hundreds MHz to these devices. However, the use of such signal frequencies in these devices has caused a significant problem that noises are produced near several GHz as harmonic thereof. Therefore, it has been strongly required to provide impedance elements and electromagnetic waver absorbers capable of attenuating and absorbing noises and electromagnetic waves having a higher frequency range near several GHz without any adverse influence on signals or electromagnetic waves having a frequency range of several hundreds MHz. In order to meet these requirements, it is necessary to not only reduce an imaginary part of permeability in a frequency range of several hundreds MHz, but also increase the imaginary part of permeability in a frequency range near several GHz.
Further, in order to use frequencies of several hundreds MHz as signals, it is required to provide an inductor element capable of exhibiting a constant high inductance in a frequency range of from low frequency to several hundreds MHz. To meet this requirement, it is also required that the real part of permeability of the inductor element is kept substantially constant without lowering in a frequency range of from low frequency to several hundreds MHz.
However, it is known that the soft-magnetic cubic spinel ferrite sintered ceramics have a so-called Snoek""s limit, so that it is not possible to reduce the imaginary part of permeability thereof in a frequency range of several hundreds MHz. Therefore, when the conventional soft-magnetic cubic spinel ferrite sintered ceramics are used as impedance elements or electromagnetic wave absorbers in electronic devices using signals having a frequency range of several hundreds MHz, there arises such a problem that the signal frequencies of several hundreds MHz required for operating the electronic devices are disadvantageously attenuated or absorbed because of magnetic loss thereof.
Also, the real part of permeability of the conventional sintered ceramics is reduced in a frequency range beyond several hundreds MHz according to the Snoek""s limit. As a result, there is caused such a problem that inductor elements using the conventional soft-magnetic cubic spinel ferrite sintered ceramics tend to be inapplicable to the electronic devices using signals having a frequency range of several hundreds MHz.
On the other hand, there have been proposed soft-magnetic hexagonal ferrite sintered ceramics having a crystal structure of Z-type ferrite, Y-type ferrite or W-type ferrite which can exhibit a small imaginary part of permeability in a frequency range of several hundreds MHz and a large imaginary part of permeability in a frequency range near several GHz exceeding the Snoek""s limit. Specifically, when the soft-magnetic hexagonal ferrite sintered ceramics are used as impedance elements or electromagnetic wave absorbers, it is possible to use signals having a frequency range of several hundreds MHz, and it is also expected to attenuate and absorb noises near several GHz which are produced as harmonic of these signal frequencies.
Further, there have been proposed soft-magnetic hexagonal ferrite sintered ceramics capable of keeping a real part of permeability thereof substantially constant in a frequency range of several hundreds MHz without lowering. Namely, when the soft-magnetic hexagonal ferrite sintered ceramics are used as inductor elements, it is possible to use signals having a frequency range of several hundreds MHz.
However, the soft-magnetic hexagonal ferrite sintered ceramics have such a disadvantage that the sintering density thereof is as low as about 4.9xc3x97103 kg/m3 at most, thereby rendering the sintered ceramics practically unusable. As to this fact, Japanese Patent Application Laid-Open (KOKAI) No. 2001-39718 describes that xe2x80x9chexagonal ferrite has a low sintering density despite excellent permeability in a higher frequency range, resulting in insufficient mechanical strength of the obtained sintered ceramics, and it has been, therefore, difficult to use the hexagonal ferrite as surface mounting parts of electronic devicesxe2x80x9d.
Since the soft-magnetic cubic spinel ferrite sintered ceramics presently used have a sintering density of not less than 5.0xc3x97103 kg/m3, it has been strongly required that the soft-magnetic hexagonal ferrite sintered ceramics also exhibit a high sintering density substantially identical to that of the soft-magnetic cubic spinel ferrite sintered ceramics. Also, the sintering density and permeability of the soft-magnetic hexagonal ferrite sintered ceramics have a specific close relationship to each other. Therefore, when the sintering density becomes lower, it may be difficult to exhibit a good permeability inherent to the soft-magnetic hexagonal ferrite sintered ceramics.
In addition, the soft-magnetic hexagonal ferrite sintered ceramics have such a disadvantage that the volume resistivity thereof is as low as 1xc3x97105 xcexa9m at most, resulting in defective insulation. As to this fact, the above Japanese Patent Application Laid-Open (KOKAI) No. 2001-39718 describes that xe2x80x9chexagonal ferrite . . . . In addition, since the hexagonal ferrite has a low resistivity as compared to spinel ferrite, it may be required to take sufficient measures for insulation upon the production of coils, resulting in troublesome production processxe2x80x9d.
Since the soft-magnetic cubic spinel ferrite sintered ceramics (Ni-Zn-based sintered ceramics) presently used have a volume resistivity of 1xc3x97106 xcexa9m or higher, the soft-magnetic hexagonal ferrite sintered ceramics have also been strongly required to have the substantially same high volume resistivity as that of the soft-magnetic cubic spinel ferrite sintered ceramics.
Further, the soft-magnetic hexagonal ferrite sintered ceramics have been required to not only have enhanced sintering density and volume resistivity, but also exhibit a small imaginary part of permeability thereof at 400 MHz and a large imaginary part of permeability at a frequency near several GHz in order to obtain impedance elements and electromagnetic wave absorbers capable of attenuating and absorbing noises and electromagnetic waves in a frequency range near several GHz without adversely affecting signals and electromagnetic waves having a frequency range of several hundreds MHz, as described above.
In addition to the enhanced sintering density and volume resistivity, in order to obtain inductor elements applicable to a frequency range up to several hundreds MHz, the soft-magnetic hexagonal ferrite sintered ceramics have been required to keep a constant real part of permeability thereof in a frequency range of from low frequency to several hundreds MHz without lowering.
Conventionally, there have been proposed various methods for improving the sintering density and volume resistivity of the soft-magnetic hexagonal ferrite sintered ceramics. In Japanese Patent Application Laid-Open (KOKAI) No. 10-92624(1998), there is described the soft-magnetic hexagonal ferrite sintered ceramics containing SiO2 and PbO, and having a sintering density of 4.6xc3x97103 to 4.9xc3x97103 kg/m3 and a volume resistivity of not less than 104 xcexa9m.
In Japanese Patent Application Laid-Open (KOKAI) No. 9-110432(1997), there is described the soft-magnetic hexagonal ferrite sintered ceramics containing SiO2 and CaO and having a sintering density of 4.6xc3x97103 to 5.3xc3x97103 kg/m3 and a volume resistivity of 1xc3x97105 to 1xc3x97106 xcexa9m.
In the above Japanese Patent Application Laid-Open (KOKAI) No. 2001-39718, there is also described the soft-magnetic hexagonal ferrite sintered ceramics containing Mn3O4, Bi2O3 and CuO.
In Japanese Patent Application Laid-Open (KOKAI) No. 2001-15913, there is described the method for producing a laminated chip element by integrally laminating a sheet or paste for magnetic layer made of soft-magnetic hexagonal ferrite having a Z-type ferrite main phase containing at least one material selected from the group consisting of borosilicate glass, zinc borosilicate glass, CuO and Bi2O3, on an Ag or Ag alloy paste for internal electrode, and then sintering the resultant laminated body at a temperature not more than the melting point of Ag or Ag alloy, i.e., at a temperature of not more than 960xc2x0 C.
At present, it has been strongly required to provide soft-magnetic hexagonal ferrite sintered ceramics not only having a high sintering density and a high volume resistivity, but also exhibiting such frequency characteristics that the imaginary part of permeability thereof is sufficiently small in a frequency range of several hundreds MHz and becomes large at a frequency near several GHz while keeping the real part of permeability substantially constant in a frequency range of from low frequency to several hundreds MHz without lowering. However, soft-magnetic hexagonal ferrite sintered ceramics satisfying such properties have not been obtained.
That is, the above Japanese Patent Application Laid-Open (KOKAI) No. 10-92624(1998) aims at obtaining the soft-magnetic hexagonal ferrite sintered ceramics having both a high sintering density and a high volume resistivity. However, the obtained soft-magnetic hexagonal ferrite sintered ceramics is still unsatisfactory in these properties. In addition, the soft-magnetic hexagonal ferrite sintered ceramics must be handled carefully since harmful PbO is contained therein.
The above Japanese Patent Application Laid-Open (KOKAI) No. 9-110432(1997) also aims at obtaining the soft-magnetic hexagonal ferrite sintered ceramics having both a high sintering density and a high volume resistivity. However, the obtained soft-magnetic hexagonal ferrite sintered ceramics is still unsatisfactory in these properties, in particular, in volume resistivity.
Further, the soft-magnetic hexagonal ferrite sintered ceramics described in Japanese Patent Application Laid-Open (KOKAI) No. 2001-39718, is improved in sintering density and volume resistivity as well as frequency characteristics of permeability thereof. However, the obtained soft-magnetic hexagonal ferrite sintered ceramics fails to show a sufficiently small imaginary part of permeability in a frequency range of several hundreds MHz.
In addition, the soft-magnetic hexagonal ferrite sintered ceramics described in Japanese Patent Application Laid-Open (KOKAI) No. 2002-15913 can be produced at a sintering temperature as low as not more than 960xc2x0 C., but fails to show a sufficient volume resistivity as described below in Comparative Example 11.
As a result of the present inventors"" earnest studies for solving the above problems, it has been found that by sintering soft-magnetic hexagonal ferrite composite particles comprising 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase, 0.3 to 10 parts by weight of barium carbonate particles and/or strontium carbonate particles and 0.1 to 5 parts by weight of silicon dioxide particles, the obtained soft-magnetic hexagonal ferrite sintered ceramics can exhibit not only a high sintering density and a high volume resistivity, but also have such frequency characteristics that the imaginary part of permeability thereof is sufficiently small in a frequency range of several hundreds MHz and becomes large at a frequency near several GHz. The present invention has been attained on the basis of this finding.
An object of the present invention is to provide soft-magnetic hexagonal ferrite composite particles used as a raw material for producing a soft-magnetic hexagonal ferrite sintered ceramics capable of exhibiting not only a high sintering density and a high volume resistivity, but also such frequency characteristics that the imaginary part of permeability thereof is sufficiently small in a frequency range of several hundreds MHz and becomes large at a frequency near several GHz.
Another object of the present invention is to provide a soft-magnetic hexagonal ferrite sintered ceramics capable of exhibiting not only a high sintering density and a high volume resistivity, but also such frequency characteristics that the imaginary part of permeability thereof is sufficiently small in a frequency range of several hundreds MHz and becomes large at a frequency near several GHz.
A further object of the present invention is to provide a green sheet containing the soft-magnetic hexagonal ferrite composite particles which is used as a raw material for producing a laminated chip element.
To accomplish the aims, in a first aspect of the present invention, there are provided soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; and 0.1 to 5 parts by weight of silicon dioxide particles.
In a second aspect of the present invention, there are provided soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; 0.1 to 5 parts by weight of silicon dioxide particles; 1 to 20 parts by weight of bismuth oxide particles; and 0.3 to 7 parts by weight of copper oxide particles.
In a third aspect of the present invention, there is provided a green sheet comprising a binder and the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; and 0.1 to 5 parts by weight of silicon dioxide particles.
In a fourth aspect of the present invention, there is provided a green sheet comprising a binder and the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; 0.1 to 5 parts by weight of silicon dioxide particles; 1 to 20 parts by weight of bismuth oxide particles; and 0.3 to 7 parts by weight of copper oxide particles.
In a fifth aspect of the present invention, there is provided a soft-magnetic hexagonal ferrite sintered ceramics having a sintering density of not less than 5.0xc3x97103 kg/m3, a volume resistivity of not less than 1xc3x97106 xcexa9m and an imaginary part of permeability at 400 MHz of not more than 1, which is produced by forming the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; and 0.1 to 5 parts by weight of silicon dioxide particles, into a compact, and then sintering the compact.
In a sixth aspect of the present invention, there is provided a soft-magnetic hexagonal ferrite sintered ceramics having a sintering density of not less than 5.0xc3x97103 kg/m3, a volume resistivity of not less than 1xc3x97106 xcexa9m and an imaginary part of permeability at 400 MHz of not more than 1, which is produced by forming the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; 0.1 to 5 parts by weight of silicon dioxide particles; 1 to 20 parts by weight of bismuth oxide particles; and 0.3 to 7 parts by weight of copper oxide particles into a compact, and then sintering the compact.
In a seventh aspect of the present invention, there is provided a soft-magnetic hexagonal ferrite sintered ceramics having a sintering density of not less than 5.0xc3x97103 kg/m3, a volume resistivity of not less than 1xc3x97106 xcexa9m and an imaginary part of permeability at 400 MHz of not more than 1, which is produced by laminating a green sheet comprising a binder and the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; and 0.1 to 5 parts by weight of silicon dioxide particles, and then sintering the resultant laminate.
In an eighth aspect of the present invention, there is provided a soft-magnetic hexagonal ferrite sintered ceramics having a sintering density of not less than 5.0xc3x97103 kg/m3, a volume resistivity of not less than 1xc3x97106 xcexa9m and an imaginary part of permeability at 400 MHz of not more than 1, which is produced by laminating a green sheet comprising a binder and the soft-magnetic hexagonal ferrite composite particles comprising: 100 parts by weight of soft-magnetic hexagonal ferrite particles containing Z-type ferrite, Y-type ferrite or W-type ferrite as a main phase; 0.3 to 10 parts by weight of barium carbonate particles, strontium carbonate particles or a mixture thereof; 0.1 to 5 parts by weight of silicon dioxide particles; 1 to 20 parts by weight of bismuth oxide particles; and 0.3 to 7 parts by weight of copper oxide particles, and then sintering the resultant laminate.